Recently, there has prevailed a hybrid electric vehicle (hereinafter referred to as HEV) jointly using an engine and an electric motor, or an electric vehicle traveling only with an electric motor. For example, the HEV is provided with two types of batteries, one type of which is a low voltage battery of about 12 volts for engine starter and car electric devices, the other type of which is a high voltage battery for driving the electric motor. The above-mentioned high voltage battery is given high voltage in such a way that a secondary cell such as a nickel hydride battery or a lithium battery is, as a unit cell, i.e., battery cell, connected in series to compose a battery pack (see, e.g., PTL 1).
The above-mentioned high voltage battery induces variation of an electrode voltage of each of the battery cells, i.e., a state of charge (SOC) as being charged and discharged repeatedly. Upon charge and discharge for the high voltage battery, in light of tolerance of each the battery cell and safety, further charging is prohibited when unit cell with the highest electrode voltage reaches the predetermined upper limit voltage, and further discharging is prohibited when unit cell with the lowest electrode voltage reaches the predetermined lower limit voltage. Therefore, usable battery capacity is substantially reduced in such an abnormal state that the variation of the SOC of each the battery cell induces. It is required that the SOC for each the battery cell is averaged and returned in a normal state in such a way that the unit cell with the highest electrode voltage in the above-mentioned high voltage battery is thereby discharged besides via the above-mentioned electric motor drive. It is also required to monitor electrode voltage of each the unit cell so as to average the SOC of such the unit cells.
The above-mentioned high voltage battery also generates significant heart by discharge of high current when driving the above-mentioned electric motor, and if certain unit cells have defect, it may thereby become in such an abnormal state as to exceed an upper limit temperature, being thereby overheated. Therefore, in order to prevent the abnormal state by stopping discharge before being in such a high temperature abnormal state, it is required to monitor the temperature of the high voltage battery. Further, since the above-mentioned electrode voltage is varied as the battery temperature varies, the above-mentioned electrode voltage is also compensated in response to the temperature.
A high voltage battery system of a conventional battery state monitoring system is shown in FIG. 21.
This high voltage battery system shown as reference sign 801 in FIG. 21 has a high voltage battery 810 as a plurality of battery packs and a battery state monitoring device 850 that monitors a state of the high voltage battery 810.
The high voltage battery 810 has a battery module 820 including a plurality of battery cells aligned in one direction, a bus bar module 830 aligned stacked on the battery module 820, wire harness 840 including a connector plug 841 and a plurality of electric wires 842.
The bas bar module 830 is provided with a plurality of bas bars 831. The plurality of bus bar 831 all connects a plurality of the battery cells 821 by connecting positive electrodes and negative electrodes that are adjacent to each other. The bus bar module 830 is also provided with a plurality of temperature sensors 832 at a middle and both ends in one direction, i.e., a direction of the plurality of battery cells 821, outputting a voltage according to the detected temperature.
Each one end of the plurality of electric wires 842 of the wire harness 840 is connected to a not-shown terminal in the connector plug 841, and the other end of which is connected to each of a plurality of terminal fittings 833 and the temperature sensors 832, the plurality of terminal fittings 833 being connected to electrodes of the battery cells 821 such as stacked on the plurality of the bus bars 831.
The battery state monitoring device 850 is provided with, e.g., a box-shaped case 851 and a controller (not shown) composed of a microcomputer that is accommodated in the case 851. The case 851 is provided with a connector socket (not shown) brought into engagement with the connector plug 841 of the wire harness 840, exposed from the case 840. By engaging the connector socket with the connector plug 841, the controller and the ware harness 840, i.e., the abovementioned terminal fitting 833 and the temperature sensors 832 are connected.
The controller has thereby detected the temperature of the electrode voltage of the plurality of battery cells and the temperature of the battery cell according to the voltage outputted via the plurality of terminal fittings 833 and the temperature sensors 832, and monitored whether or not each of the high voltage batteries 810 is in a normal state.